That wouldn't work for much of the South where summer usage for a house can easily hit 100 kWh/day for air conditioning. The hottest part of the day usually starts at about the end of the prime solar hours. Plus you'll want massive overcapacity of your batteries as deep discharges drastically reduce their useful lifespan.
Wow - that's a crazy amount of energy. As a Brit who's never been the south of the US, is that figure really true? 100kWh is about 300 miles in a Tesla, or boiling a kettle constantly for about 30 hours.
If that's really accurate, then I'm staggered at how much energy folks must be using to keep cool, and makes my efforts at saving energy seem paltry in comparison.
Yes, that is a crazy amount. I live in the South, and the highest we hit is about 35kWh on extremely hot weekend days. Our typical summertime use is more like 20kWh/day -- but according to our utility, we're using about 1/2 of what a typical neighbor uses.
Based on this very scientific single-neighborhood sample, I'd guess 40-60kWh/day would not be unusual during the peak summer months.
In the US, there are very large variations in house interior volume, insulation, and usage patterns. Upper-middle class house built on a slab with standard in Dallas with a stay-at-home mom, for example? I wouldn't bat an eyelash at 100kWh/day on the hottest and wettest days. Condo apartment in downtown Houston? That would be excessive.
US insulation requirements in Dallas is R-20 in the walls [1]. The PassivHaus standard is R-40 to R-60. I believe Germany requires R-5 at a minimum. Mainstream US construction design and practice still doesn't account for thermal bridging, so that defeats much of the insulation we're throwing into our buildings.
Swamp coolers work in areas that are hot and dry, like New Mexico or Arizona.
They do not work well if it's hot and humid, for two reasons. One is that the water doesn't evaporate as well, so they don't cool well. The other is that the whole point is comfort, and in a humid climate you don't achieve that unless you remove both heat AND humidity, but swamp coolers add humidity.
Texas has some desert areas (western part of the state), but most of the population lives in the part of the state that isn't a desert.
The good news is with modern construction techniques and equipment, you can cut energy usage WAY down. You can cut energy usage a lot with stuff like a radiant barrier in the attic, attic vents, lots of insulation, double pane windows, a "tight" house with little air leakage, proper angles to keep direct sun from heating up the house at the wrong times, and a high-efficiency AC unit that you service and maintain properly. In fact, a lot of those things are actually more beneficial than getting solar panels.
I live in New Jersey and just had solar panels installed on my roof. Peak power is about 7.8 KW. On clear days, power production in the summer is about 50 kWh
I have been keeping daily logs this summer and find that my daily power consumption swings between about 25 kWh on cool days to 65 kWh on really warm days. Definitely a lot lower than 100 kWh mentioned previously.
I spent much of last year in Southeast Asia within ten degrees of the equator and rarely had A/C. It wasn't a problem for me, though my computer was often unhappy.
I went to Egypt as a teenager and remember the temperature in Sharm el Sheikh cracking 50C. We would literally sprint from the A/C in the hotel across the beach to the water because the sand was too hot to walk.
Equivalent latitude doesn't mean equivalent climate. As an example, which of these cities is further north, Buffalo, NY, USA or Cannes, France? Hint: it's the one known for topless sunbathing, not the one known for sub-zero outdoor football games.
According to WolframAlpha, the hottest temp on record in Cairo is 118°F, while Phoenix, AZ has hit 123°F. Even the average high is 5°F higher in Phoenix.
I can't find where the site now, but there was a fairly compelling argument that it was overall still more energy efficient for people to live in Arizona and AC dropping the temp from 90F to 70F than to live in a northern state where for 6 months out of the year you have to heat the house from 20-40F up to 70F.
A/C efficiency ("power factor") is measured using the ratio of heat (energy) moved outside to the amount of energy put into the air conditioner , which is usually >> 1 unless there is a huge temperature difference between inside and outside.
An ideal furnace has a 1:1 ratio of heat energy injected into the house to energy used to run the furnace. Heat pumps can get over 1:1 ratios, but come with caveats and are more expensive than A/C units.
Also, you can make it feel cooler with a dehumidifier, which often is more efficient than cooling. For furnaces, you need a sweater, but your article assumed a 70F indoor target.
Let's not get ahead of ourselves, 100kWh is not the "low limit" of how much energy you need to get an temperature controlled home in the South for a day.
This is the figure in an environment where electricity costs nothing and there is zero pressure from home design to the actual AC unit to reduce consumption. Let's face it, this attitude isn't going to fly in the future. You could probably cut that figure by a good 10% by installing your choice of solar panels or a bunch of trees, just from less sun hitting the structure.
(Cut it in half if you consider the average American in the South lives in a freakishly large house fit for a queen with entourage and is cooling all of it..)
> That wouldn't work for much of the South where summer usage for a house can easily hit 100 kWh/day for air conditioning.
It should be noted that peak energy expenditure for air conditioning happens more or less at exactly the moment when the influx of energy from the Sun is also at its peak. That's, like, a gigantic hint that mother nature is dropping on you, hoping you'll notice it. The disease, and its cure, are gushing forth from the same place at the same time.
Probably most of the energy for air conditioning in the future will not come out of storage, but it would be produced at the moment when it's consumed, by solar panels or some other solar technology.
For those interested in more info on this, it's called Temperature Lag. There's also the related phenomenon of Seasonal Lag, which is where the hottest part of the year comes somewhat after the period of maximum solar radiation, not during it.
It's only prime solar hours if you point your solar panels due south. That gets you a higher figure on paper, but if you need the power later in the day you could point them a bit more to the west and get a lot more usable power when you need it. With solar panel prices falling, it's a race to see if it's cheaper to over-provision solar panels or batteries.
I would think that for that use case, using thermal storage should be more efficient? Don't store electricity to run AC later, but run AC to cool down water or the ground beneath your house or something, and then cool your house with that later.
Or build something like an Earthship (http://earthship.com/). I know that these can air condition a house in New Mexico through geothermal heat transfer, however no idea how they handle the more humid summers of the South East.
They work, but aren't as comfortable as in drier climes. Humidity is tough to control with low-energy, low-maintenance solutions. Unfortunately, many people's discomfort perceptions are heavily influenced by humidity.
I recently moved from Nashville (quite humid) to Flagstaff (quite dry) and the difference is amazing. Large temperature swings are barely noticeable in the dry climate, but would require substantial changes in weight of clothing in the humid one.
That would require a huge amount of work and expense, and at the end of the day cold water isn’t very good at cooling off giant masses of air and furniture.
This digit is unbelievable. A good aircon can pump 4 gigacalories per hour using 1kw/h while running at full power with +40C and 40% humidity outside.
5gkal per hour is more than enough to keep a 50m2 room with huge windows at 21-22C in scorching heat.
If your house is huge, like 200m2 McMansion, and your ventilation does no recuperation whatsoever, and you have near nil heat insulation (like most of housing in US,) you will barely use 50kw/h per day even if you live in the middle of Sahara
A well insulated water tank that is electrically chilled during peak solar and used to cool down air later in the day/night could solve that storage problem without any cell degradation. Theoretically, with perfect insulation, this could even reduce the total electricity demand, when the conversion from electricity to a temperature gradient happens during a time when the base temperature is low.
I would have thought that heating would require a lot of energy in the Nordic countries - but perhaps that doesn't use much electricity? I live in the NW US, in a heavily-insulated passivhaus with a 5kW PV array on my roof, and my average usage is 13kWh / day (though I am also charging a PHEV vehicle's battery some days, and still using an ineffecient old hex-core Xeon workstation on top of heating and cooling, heating water, cooking etc.).
Electrical heating is not used when it can be avoided. It is much better to use waste heat from energy production and industry to heat your home: https://en.wikipedia.org/wiki/District_heating
If it's 10 cents per kWh, that's only 10 dollars per day or 300 per month.
Investing in insulation or other things might or might not make sense.
High electricity price for a long future period would also encourage investment.
Alternatively, constructing your house in a benign climate, if you do a lifecycle analysis and look at the upkeep cost.
Even if the hottest part of the day is past prime solar hours, with a solar system you won't be discharging the battery as fast since the system will be powering the AC for most the day. Also, with that much usage, it might be time to investigate insulation.
